Fourteen-year-old Yusuke Urameshi is the toughest kid in town and the worst student at Sarayashki Junior High. But despite his constantly getting into fights and cutting class, he's not really as bad as you might think. He is a misunderstood kid with a terrible home life. He lives with his mother who is an unemployed, alcoholic. Kayko is Yusuke's only close friend. She is the polar opposite of Yusuke and is one of the leading students at her school. One event will change Yusuke's life forever. He sacrifices his life by saving a child from an oncoming car. Is this 14 year old's life really over?

Yusuke suddenly finds himself greeted by Botan, a spirit messenger who guides Yusuke into the Spirit World to see the ruler, King Yama. Koenma, the king's son, is in on the throne because the king is away on vacation. Because of Yusuke's ultimate sacrifice, Koenma offers him a second chance at life. In order to return to the Living World, Yusuke must become a 'Spirit Detective.' Koenma assigns Botan to assist and guide Yusuke in his new role.

Yusuke makes his return to the Living World and receives his first assignment as a 'Spirit Detective.' He must track down three demons who have stolen some very powerful and dangerous artifacts from King Yama's vault. But these three demons aren't going to sit quietly, waiting to be found. Rather, they decide to strike first, and attack Yusuke where he is most vulnerable - Kayko! Can Yusuke recover the artifacts from these formidable foes? And more importantly, can he save his friend?

Without time to relax, Yusuke receives his second assignment. An aging Martial Arts expert named Genkai is going to pass along her knowledge to one worthy student. Koenma fears that a demon named Rando is planning to disguise himself in order to become the selected student. Yusuke must discover Rando and stop him. Rando is extremely dangerous and has already killed 99 martial arts experts for the sole purpose of stealing their techniques. Genkai's knowledge would make Rando virtually unstoppable. Genkai narrows her applicants to eight finalists who will face off in a tournament. Yusuke must use his detective skills to discover which of these eight fighters is the disguised demon. But even if he finds him, how is he going to stop a monster with 99 lethal fighting techniques?

Yusuke returns to his friends after six months of excruciating training with Genkai. He is sharp and has mastered many new techniques. Botan immediately shows up to give Yusuke his next assignment. Thousands of Makai insects have been released in the Living World. If not stopped, these creatures will infect untold numbers of human hosts and turn them all into mindless zombies. Yusuke must destroy the insect whistle that controls the Makai. To do this, he will have to defeat the Four Saint Beasts who possess the whistle. Koenma has sent two newcomers, Kurama and Hiei, to join Yusuke and Kuwabara on their quest. Kurama is over 300 years old and holds a wealth of wisdom. Hiei, a master swordsman, possesses incredible strength, speed, and a mysterious third eye called the Jagan. Now this unlikely team must band together for their assault on Maze Castle, the home of the Four Saint Beasts. But time is running short, for with every new Makai insect that enters the Living World, the Four Saint Beasts tighten their stranglehold on humanity!

Yusuke's next assignment could prove to be his most dangerous. An evil man named Gonzou Tarukane has kidnapped an apparition named Yukina. Yukina's tears turn into beautiful jewels that Tarukane plans to sell. Yusuke, Botan, and Kuwabara are sent to rescue Yukina from his grasp. Unfortunately, Tarukane has hired the dreaded Toguro Brothers to guard Yukina. After defeating many attackers, Yusuke and Kuwabara finally stumble upon the Toguro Brothers. The two quickly gain the upper hand on the Toguro Brothers, but the revelation of their secret power puts Yusuke and Kuwabara in danger of losing more than just the fight!